Optical fibres terminated by connectors and the receptacles which are adapted to received these connectors are an important part of virtually any fibre optic communications system. For example, such connectors and receptacles may be used to interconnect fibre segments to create longer lengths, to connect optic fibre to active or passive devices, etc. However, in some cases, for example for security reasons or in order to better manage a telecommunications network, it is desired to physically limit the insertion of a connector plug into a particular receptacle socket, and as a result prevent the transmission of data via that connector plug and receptacle socket.
The prior art reveals a variety of systems for preventing a connector plug from being inserted into a receptacle socket. One of these prior art systems comprises at least one tab arranged at a certain position on the connector plug, each of which is adapted for insertion into a corresponding tab receiving indentation moulded in the receptacle socket. In the absence of such a hollow the tab buts against the opening of the receptacle socket, thereby preventing the connector plug from being completely inserted into the receptacle socket, thereby preventing the connector plug from being correctly interconnected with the receptacle socket. One drawback of these prior art designs is that that the tab, being typically moulded into the plastic connector plug housing, can be easily removed by filing or using a sharp blade or the like. Another drawback is that such prior art designs only allow two types of connector plugs to be differentiated between: connector plugs with a tab and connector plugs without a tab.
The prior art also reveals keying systems such as the U.S. patent application Ser. No. published with the No. 2002/0126960 A1 comprising a connector plug and receptacle socket. Interconnection of the connector plug and receptacle socket is limited to connector plug/receptacle socket pairs where a key within the receptacle socket mates with a corresponding key receiving slot in the connector plug. A connector plug with a key receiving slot in one position is unable to interconnect with receptacle sockets with a differently positioned key. As a result, by providing a number of differently positioned keys and key receiving slot a system of selective interconnection between connector plugs and receptacle sockets can be arrived at. These systems, however, are generally impractical in many fibre optic systems given the relatively small size of the connector plug and the receptacle socket.